The present invention relates to a dual pump system, and more particularly, to a dual pump system which is capable of bypassing a portion of oil, when the oil supplied to an engine excessively increases in supply pressure, to always maintain an adequate oil supply pressure at each portion of the engine.
Generally, engine oil is circulated through an engine of a vehicle to prevent the engine from being overheated or reduce frictional force between various mechanisms. For this, an oil pump is applied.
However, driving torque of the engine may be lost when the oil pump operates because the oil pump discharges oil to a discharge-side, and simultaneously, operates to suction oil that is retuned to a suction-side.
In vehicles, since the improvement in the driving torque of the engine is essential to improve fuel efficiency, the driving torque loss (power consumption consumed for supplying oil) due to an oil pump, which is proportional to the relationship of “flow rate×hydraulic pressure”, may be reduced by improving performance of the oil pump.
In recent years, the importance in fuel reduction of the vehicles is further emphasized by high oil prices and the regulation of carbon dioxide, and thus the improvement of the fuel efficiency and the eco-friendliness are being considered to key factors when the vehicles are developed.
Particularly, when considering the fact in which the improvement of the driving torque of the engine is essential, the reduction of the driving torque through the oil pump may be very effective to improve the fuel efficiency.
For example, as illustrated in FIG. 1, a structure, in which a portion of oil is bypassed through a relief valve at a high speed RPM to reduce an oil pressure and improve fuel efficiency, is disclosed.
The oil pump as described above may reduce the oil pressure in the high speed section. However, since the oil pressure is maintained to a high level as ever in a middle speed section, the improvement of the fuel efficiency may deteriorate.